Electric pressure head



June 21, 1949. c M TH w 2,474,146

ELECTRIC PRESSURE HEAD Filed July 31, 1946 fizz/1972 5 07 flauci efffiaz fiawa y Patented June 21, 1949 UNITED STATES PATENT OFFICE ELECTRIC PRESSURE HEAD Claude M. Hathaway, Denver, 0010.

Application July 31, 1946, Serial No. 687,483

6 Claims. 1

The present invention relates to electric pressure heads, or more particularly to an electric pressure head employing a strain-responsive wire element.

Heretofore it has been proposed to obtain indications of the pressures developed within an internal combustion engine by means of a pressure head which is connected in an electric circuit to give an indication of the high rate at which pressures develop in an engine. In certain engine tests, it is particularly desired to have an indication of predetonation action and presure heads of the electrical type are particularly suited for observation of this phenomenon. The pressure heads heretofore employed, however, have commonly been of the electromagnetic type or of'the piezoelectric crystal type; Both of these types have certain disadvantages, particularly with respect to changes induced by temperature. In the design of the electromagnetic head, it is necessary to introduce compensations for temperature variations and to provide a relatively elaborate supporting means to minimize the effect of temperature variations. The piezoelectric crystal units must also be protected against temperature variations beyond certain limits since the crystal may change in characteristic if elevated in temperature beyond a certain amount. It, therefore, would be desirable to obtain a different type of gauge which is not subject to the aforementioned disadvantages.

In accordance with the present invention it is proposed to provide a pressure head which employs a strain-responsive resistance element. The pressure head constructed in accordance with the present invention is readily compensated for balancing out temperature effects.

It therefore is an object of the present inven tion to provide an improved electric pressure head particularly suited for use with internal combustion engines.

It is a further object of the present invention to provide an improved electric pressure head employing a resistance wire strain-responsive element.

It is a further object of the present invention to provide an improved electric pressure head which may be connected in an electric bridge circuit for indicating transient pressures.

Other further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawing, wherein:

Figure 1 is a view of a pressure head con- 2 structed in accordance with the present invention;

Figure 2 is another view of a pressure head constructed in accordance with the present invention, which has been provided with a protective shield or covering; and

Figure 3 shows an electric circuit diagram, to which is connected a pressure head of the type illustrated in Figures 1 and 2.

Referring more particularly to the drawing, it will be seen that there has been shown in Figure 1 an electric pressure head base formed of metal having an upper cylindrical portion I l and a lower threaded portion l2. Immediately above the threaded portion l2 there is provided a hexagonal portion l3 which is adapted to be engaged by a wrench for the insertion of the pressure head into a suitableopening in an internal combustion engine. The lower portion of the pressure head II is provided with a central hollow aperture I4 so that the lower half of the cylindrical portion ll may be subjected to stress corresponding to the pressure developed within the internal combustion engine. Immediately above the hexagonal portion I3 there may be provided a shoulder l5, cylindrical in form, for receiving a protective cover It, which is shown in Figure 2.

The upper solid portion of the cylindrical body portion ll of the electric pressure head has wound thereabout a number of turns of strainresponsive resistance wire H. A similar number of turns of strain-responsive wire l8 are wound about the lower half of the cylindrical portion I I so as to be in the proximity of the relativelythin walls formed by the central aperture ll. The lower resistance unit ill will be responsive to the strain induced in the walls due to the pressure within the aperture or cavity H. The upper resistance element I! will not be subjected to any stress or strain because the cylindrical portion II is' solid. The upper portion [1, however, will be subjected to the same temperature as the resistance unit It because of the conduction of heat along the body ll. Thus, the effects produced in the strain-responsive unit I8 due to temperature are also being produced in the resistance wire unit I1.

Suitable resistance wire for this purpose has been available on the market under various trade names. An example of such wire is Advance wire which has a favorable ratio of strain sensitivity. While units l1 and I8 may be retained in position on the cylindrical portion II in any suitable manner, a lacquer or paint which is capable 3 of withstanding the temperatures to which the body H is subjected may be employed or the resistance units l1 and I8 may be secured in position by some form of vitreous coating. The upper terminal of the resistance unit is and tin lower terminal of the resistance unit ll may be connected to an electric connection is mounted on a protective covermg It. The upper terminal of the resistance unit H is connected to another.

electric terminal 2i, whereas the-lower terminal of the resistance unit i8 is connected to another electric terminal 22. The cover it may be employed to give protection to the resistance units I! and I8 since they are of relatively small diameter of wire. The cover IE will also serve to ensure that the upper resistance unit I1 is subjected to the same temperature as the lower resistance unit l8, particularly in the instance where the unit may be subject to drafts.

Figure 3 shows a circuit diagram wherein the resistance units l1 and I! are connected in a bridge circuit which includes a tapped primary winding 23 of a transformer 24. The central tap of the primary winding 23 of the transformer is connected to one side of an alternating current source which has its other side connected to a common juncture between the resistance units l1 and it. The transformer 24 has secondary winding 25, which is connected to a vacuum tube amplifier 26 which has its output connected to an indicating instrument 21. If desired, the indicating instrument 2'! may be of any suitable type, such as a physical indicating instrument, or a recording instrument.

While for the purpose of illustrating and describing the present invention, a certain embodiment has been illustrated in the drawing, it is to be understood that the invention is not to be limited thereby, since such variations in the "instruments employed and in their arrangement and configuration are contemplated as may be commensurate with the spirit and scope of the invention set forth in the following claims.

I claim:

1. An electric pressure head comprising an elongated member having a chamber at one end adapted to be connected to a source of pressure, a strain-responsive wire element mounted about the exterior of said member in the proximity of said chamber, and a similar strain-responsive wire element mounted on a portion of said member which is not subjected to stress or strain due to pressure within said chamber.

2. An electric pressure head comprising a cylindrical member having a solid portion and a hollow portion, said hollow portion being provided with means for supplying pressure thereto, a strain-responsive wire element mounted on the exterior of said hollow portion of said cylinder, a similar wire strain-responsive element mounted 4 on said cylinder about said solid portion, and means for connecting said strain-responsive elements to a balanced bridge circuit.

3. An ambient temperature compensated elec tric pressure head for internal combustion err-- gines comprising a cylindrical body member having hollow and solid portions, 9. pair of strainresponsive resistance wire elements wound about the exterior of body member in the proximities of said hollow and solid portions, and means for connecting said elements to a source of alternating potential and to a balanced bridge circuit.

4. An ambient temperature compensated electric pressure head for internal combustion engines comprising a cylindrical body member having hollow and solid portions, a pair of strainresponslve resistance wire elements, one element being wound about the hollow portion of said body member, the other being wound about the solid portion of said body member, and means for connecting said hollow portion in communication with the combustion chamber of an engine.

5. An ambient temperature compensated elec tric pressure head for internal comb -"istion engines comprising a cylindrical body member having hollow and solid portions, a pair of strain-responsive resistance wire elements, one element being wound about the hollow portion of said body member, the other being wound about the solid portion of said body member, means for connecting said hollow portion in communication with the combustion chamber of an engine, and means surrounding said body member to shield said elements from air currents.

6. An ambient temperature compensated electric pressure head for internal combustion engines comprising a cylindrical body member having hollow and solid portions, a pair of strain-responsive resistance wire elements, one element being wound about the hollow portion of said body member, the other being wound about the solid portion of said body member, means for connecting said hollow portion in communication with the combustion chamber of an engine, and means surrounding said body member to shield said elements from air currents, said means being provided with electrical connections for connecting said elements in a balanced bridge circult.

CLAUDE M. HATHA'WAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,420,148 Ostergren May 6, 1947 2,421,907 Postlewalte June 10, 1947 Disclaimer 2,474,146.C'lauda M. Hathaway, Denver, Colo. ELECTRIC Pnnssunn Hm. Patent dated June 21, 1949. Disclaimer filed July 29, 1950, by the inventor.

Hereb enters this disclaimer to claims 1 and 2 of said patent.

[ Gazette August 22, 1950.]

Disclaimer 2,474,146.-Ulaude M. Hathaway, Denver, Colo. Ennc'rmc PRESSURE Hm. Patent dated June 21, 1949. Disclaimer filed July 29, 1950, by the inventor.

Hereb enters this disclaimer to claims 1 and 2 of said patent.

[ Gazette August 22, 1950.] 

